Epoxy resins are frequently used in the production of fiber reinforced plastic pipe. An epoxy resin will cure or crosslink by itself when heated, but the time and temperature required are impractical for commercial operations. To achieve practical results, curing agents and accelerators are used. The curing agent will crosslink with the epoxy resin to become a chemical part of the cured resin, while the accelerator will either promote the reaction of the epoxy resin and curing agent or will serve to catalyze the reaction of the epoxy resin itself.
It is well known to employ hydroxyl groups as curing agents for epoxy resins. However, this reaction is very slow and it has been customary to accelerate the action by using small amounts of an inorganic acid, such as phosphoric acid. The disadvantages of this type of acceleration is that it promotes an etherification reaction which takes place with the formation of water. While the formation of water may be of little consequence in a paint or coating application where the layers are thin, formation of the water during curing of a filament wound article, such as a pipe, results in the entrapment of water within the walls of the pipe and produces a serious reduction in the physical properties of the pipe.
It is also known, as disclosd in U.S. Pat. No. 2,575,558, to utilize a tertiary amine, such as triethylamine, as a curing agent for epoxy resins. Tertiary amines as curing agents are normally used in fairly high concentrations and it is assumed that the reaction is an epoxy-epoxy polymerization.